1. Field of the Invention
The present invention relates to a driving apparatus for driving the spindle or the workpiece pallet of an electroerosive machining apparatus to a rotational movement.
It is well known in the art that an electroerosive machining apparatus ensures an extremely precise machining of workpieces by removing workpiece material under the effect of electro erosion. In order to achieve an accurate shaping of a workpiece, the parts and elements of the electroerosive machining apparatus have to be manufactured and must operate with at least an equal precision, if possible with an even higher degree of precision than the desired accuracy of shaping of the workpiece.
In the case of e.g. a spark erosion machining apparatus, an electrode is used to machine the workpiece, said electrode being received in a spindle of the apparatus and can be raised and lowered as well as rotated. A driving means is provided to rotate the spindle and thereby the electrode, said driving means usually comprising an electric motor. In order to displace the electrode into a desired angular orientation, the spindle is rotated by the electric motor via a reduction gearbox.
2. Prior Art
One of the main problems in connection with known driving devices of the kind referred to hereinabove is the transmission backlash between motor shaft, gear box and spindle. Thus, one was forced to use extremely precisely manufactured reduction gear boxes and power transmission elements in order to achieve the desired high positional accuracy of the angular position of the spindle. Such a driving apparatus, however, is very expensive, requires a frequent maintenance and is subject to wear out comparatively quickly; thus, the precision to be achieved is impaired. The same facts are true for a driving apparatus for the rotation of workpiece pallets.